The present invention relates to the medical arts. It finds particular application in cardiac assist technologies using, for example, rotodynamic blood pumps, also known as left ventricular assist devices (LVAD) in assisting patients with failing hearts and will be described with particular reference to a centrifugal blood pump. It is to be appreciated that the present invention is also applicable to other types of pumps, such as axial flow pumps, and is not limited to the aforementioned application.
Electrically driven rotodynamic pumps (axial flow, mixed flow and centrifugal) have prospective applications in cardiac assist technologies. A typical cardiac assist system includes the blood pump itself, electrical motor (usually a brushless DC motor integrated into the pump), drive electronics, microprocessor control unit, and an energy source, such as rechargeable batteries. These pumps are used in fully implantable systems for chronic cardiac support. In this case the whole system is located inside the body and there are no drive lines penetrating the skin. For temporary support, and as well as for the bridge-to-transplant application, the pump itself is also located inside the body. However some system components including drive electronics and energy source may be placed outside the patient body.
Both chronic and temporary patient support require controlling the pump performance to satisfy the physiologic needs of the patient while maintaining safe and reliable system operation.
The primary goal for cardiac assist control is to provide an adequate blood pump flow rate for the patient that may depend on various physiological and psychological factors. Prior systems have pressure sensors, or ECG sensors external to the pump to determine the heart rate and blood pressure of the patient. These systems require extra hardware inside the patient and increase the risk of complication.
U.S. Pat. No. 5,888,242 to Antaki et al. discloses a rotodynamic ventricular assist pump that uses current measurements and pump rotations per minute (rpm) measurements to test and identify a maximum rpm that will not cause ventricular collapse. The invention described in this patent monitors for a current spike indicative of ventricular collapse, and in response decreases the pump speed. It does this iteratively to achieve a maximum average flow rate. This approach puts unnecessary strain on the heart by continuously depending on this dangerous situation to optimize pump flow.
The present invention provides a new and improved method and apparatus that overcomes the above referenced problems and others.